Fractures:

When a rabbit favors one of its limbs, remains in a corner, and acts apathetic, it is very possible that the animal suffers from a broken limb. Broken bones are usually from an elevated place or stepping on it accidentally or when it is caught in a closing door. Such accidents can even result in spinal injuries and paralysis.
Hairline fractures heal by themselves; for simple fractures consult a veterinarian; for compound fractures your veterinarian may recommend humane euthanasia.